Counterflow preheating means for a concurrent countercurrent grain dryer

ABSTRACT

A concurrent-countercurrent flow column grain dryer of the type having an enclosed bin with a wet grain inlet at the top and a dry grain outlet at the bottom includes means for introducing hot air as a drying medium for the grain in a flow concurrent with the grain. Means are also provided at the bottom of the bin to introduce cool air which flows countercurrent to the grain flow. A first exhaust is provided intermediate the points where hot and cool air are introduced. A second exhaust positioned above the hot fluid inlet ducts also exhausts hot air flowing upwardly from the hot fluid inlet ducts in a countercurrent direction to the downward flowing grain and preheats the wet grain immediately after the wet grain enters the enclosed bin.

United States Patent 1191 Meiners et al.

C OUNTERFLOW PREHEATING MEANS FOR A CONCURRENT COUNTERCURRENT GRAIN DRYER Inventors:

Assignee:

Filed:

Appl.

Elmo R. Meiners, Anchor; John 0.

Bradford, Gibson City, both of 111.

said Meiners, by said Bradford Apr. 12, 1971 References Cited UNlTED STATES PATENTS Kline et a1. ..34/33 Graham ..34/13 Foster ..34/ 1 70 Randolph .34/174 Apr. 17, 1973 [57] ABSTRACT A concurrent-countercurrent flow column grain dryer of the type having an enclosed bin with a wet grain inlet at the top and a dry grain outlet at the bottom includes means for introducing hot air as a drying medium for the grain in a flow concurrent with the grain. Means are also provided at the bottom of the bin to introduce cool air which flows countercurrent to the grain flow. A first exhaust is provided intermediate the points where hot and cool air are introduced. A second exhaust positioned above the hot fluid inlet ducts also exhausts hot air flowing upwardly from the hot fluid inlet ducts in a countercurrent direction to the downward flowing grain and preheats the wet grain immediately after the wet grain enters the enclosed bin. 1

5 Claims, 2 Drawing Figures PATENTED 75' 3.727, 323

' INVENTORS:

ELMO R. MEINERS JOHN G. BRADFORD BY.- (iMM,d/Z&M/f M W ATT'YS COUNTERFLOW PREHEATING MEANS FOR A CONCURRENT COUNTERCURRENT GRAIN DRYER BACKGROUND OF THE INVENTION This invention relates to an improvement in a grain dryer. In particular, it relates to an improvement in a concurrent-countercurrent flow type grain dryer of the type disclosed in copending application Ser. No. 104,305, for a GRAIN DRYER WITH IMPROVED GRAIN DEFLECTOR, filed Jan. 6, 197] by Charles Rathbun.

Grain, partilcularly corn, is now often dried before storing to prevent wet pockets, mildew and consequent spoilage of the grain. Fast, efficient drying may be effected by the introduction of a generally heated, low moisture content drying medium (usually air) to the wet grain. The drying medium is moved relative to the grain and accumulates moisture from the grain. The moisture saturated drying medium is then removed from contact with the grain with the result that the grain has a relatively lower moisture content.

However, because the drying medium is usually heated to effect moisture transfer, sudden transition in the temperature of the grain will result and may cause poor grain conditioning of the grain kernels. For example, the sudden transition and exposure of the grain from a relatively cool or ambient temperature to the high temperature of the drying medium may cause the grain to become scorched. That is, subjecting the cool grain to a hot (approximately 300 F.) blast of air will quickly evaporate moisture from the grain at and near the surface of the grain kernels. Simultaneously, very cooling of the moisture at or near the surface of the kernel.

Thus, such prior art'systems may cause scorching of the grain particularly when the ambient temperature of the grain is very low. Typically, ambient grain temperatures are very low during the late fall in the Midwest when outdoor temperatures are well below freezing.

To avoid such problems, the grain could be heated slowly. However, such a procedure would generally have to be done on a batch basis and would not be as efficient as continuous drying systems. Also, batch drying would be more expensive. Thus, in order to be commercially appealing, an improved drying apparatus which avoids scorching problems should be a continuous drying apparatus.

Concurrentcountercurrent grain dryers constitute a class of continuous type grain dryers which are very efficient and which normally do not produce an excess of cracked grain. Such dryers are continuous type dryers since grain continuously enters an inlet at the top of a drying bin and flows downwardly past upper hot air ducts, intermediate exhaust ducts, lower cool air ducts and out the bottom of the bin. The hot air flows concurrent with the grain to the intermediate exhaust duct. Cool air from the lower cool air ducts flows upwardly counter to the grain flow and exits at the same intermediate exhaust duct.

Although concurrent-countercurrent dryers are very effective, nevertheless when grain introduced at the top of the bin is especially cold due to the ambient conditions external the dryer, scorching and generally poor grain conditioning is quite likely to occur. That is, when a great temperature or moisture differential exists between the ambient condition grain and the drying medium, scorching will probably occur. Of course, scorching of the grain will undesirably reduce the value of the grain. Therefore, it is an object of this invention to provide an improved concurrent-countercurrent grain dryer which provides a means for preheating the grain to thereby avoid scorching and to provide better grain conditioning.

SUMMARY OF THE INVENTION In a principal aspect, the present invention comprises a grain dryer of the type having an enclosed bin with a wet grain inlet and dry grain outlet, and a plurality of spaced horizontal hot fluid inlet ducts provided for directing fluid drying medium downwardly through a continuously moving bed of grain. Below the hot fluid inlets are a plurality of spaced horizontal cold fluid inlet ducts for directing a fluid cooling medium upwardly and through the same bed of grain. The cold fluid inlet ducts are spaced from one another to provide a plurality of grain discharge outlets. To provide for continuous downward grain bed movement or flow, means are provided for adding wet grain through the wet grain inlet, and means are also provided for removing dry grain from the grain outlets. Intermediate the hot and cold inlet ducts is a set of horizontal exhaust ducts for receiving and exhausting drying fluid medium flowing from the hot and cold fluid inlets. Means are supplied for providing hot fluid to the hot fluid inlet ducts and cold fluid to the cold fluid inlet ducts. A second set of upper horizontal exhaust ducts are provided above the hot fluid inlet ducts. These upper exhaust ducts receive and exhaust hot fluid medium from the hot inlet ducts in a direction countercurrent to the grain flow. This countercurrent flow of hot air preheats the downward flowing grain as it enters the bin and substantially prevents scorching.

It is thus an object of the present invention to an improved grain dryer.

Another object of the present invention is to provide means to eliminate scorching, shattering of the wet grain in a column type, continuous grain flow, concurrent-countercurrent grain dryer.

It is a further object of the present invention to provide an improved concurrent-countercurrent grain dryer wherein means are provided to preheat cold or wet grain and prevent scorching of the grain.

These and other objects, advantages and features of the present invention will be set forth in greater detail below.

provide BRIEF DESCRIPTION OF Til-IE DRAWING In the detailed description which follows, reference will be made to the drawing comprised of the following figures:

FIG. 1 is a cut-away perspective view of the improved concurrent-countercurrent flow, column type grain dryer of the invention; and

FIG. 2 is a cross-sectional view of the improved column type concurrent-countercurrent flow grain dryer embodying the present invention.

DESCRIPTION OF-THE PREFERRED EMBODIMENT Referring now to the figures wherein like numbers refer to like parts, in FIG. 1 the improved concurrentcountercurrent flow column type grain dryer of the invention is shown generally as 10. Grain dryer includes a completely enclosed bin having a top 12 which includes upward sloping surfaces 14 and 16, sides 18 and 20, and exterior end walls 22 and 24. A wet grain inlet auger 17 is located beneath the apex formed by surfaces 14 and 16. The bin is supported on stand 26.

In FIG. 1 a portion of the upward sloping surface 14 and side wall 18 is cut away to illustrate the interior construction of the dryer 10. Hot air inlet ducts 28A, 28B, 28C, 28D and 28B are shown in parallel relationship with side walls 18 and 20. Ducts 28 extend through an internal end wall 21, center support brackets 23, 25 and 27 and through the exterior end wall 24. Ducts 28 include vertical side walls 30 and 32, a pair of inclined top surfaces 33, 34 and an open underside 36. Ducts 28 lie in a common horizontal plane and are not perforated.

Six enclosed parallel spaced cool air ducts (40A-40F) are located below hot air inlet ducts 28 and above a grain outlet auger 50 which will be hereinafter described. Ducts 40 are parallel to the hot air inlet ducts Ducts 40A and 40F are semi-triangular in cross section, whereas ducts 40B through 40B are triangular in cross'section.

Adjacent cold air inlet ducts are spaced from one another to define five grain discharge outlets 41A through 41E. Grain discharge outlets 41A through 41B are positioned directly vertically below each hot inlet duct 28A through 28E, respectively. Metering rolls A through 45E are located below grain discharge outlets 41A through 41E, respectively, to control the gravitational flow of grain downward through the dryer.

Intermediate the hot air inlet ducts 28 and cold inlet ducts 40 are a plurality of exhaust ducts 44 positioned traversely to the hot and cold inlet ducts 28 and 40. Ducts 44 serve to exhaust selected portions of the hot air and all the cold air introduced by inlet ducts 28 and 40, respectively.

The grain dryer bin has a bottom consisting of downward sloping surfaces 46 and 48. The dry grain outlet auger is located at the bottom of the bin where downward sloping surfaces 46 and 48 meet. Auger 50 runs parallel with the length of sidewalls 18 and 20. Rotating metering rolls 45 (45A-45E) serve to continuously remove measured amounts of grain from the bin. This grain is ultimately discharged from the bin by auger 50.

The improvement of the present invention comprises a plurality of two parallel spaced hot air exhaust ducts 38A and 383 located near the top of the bin. Ducts 38 are above and parallel to hot air inlet ducts 28. Ducts 38 receive and exhaust hot fluid air flowing countercurrent to grain flow from ducts 28A through 28E. Ducts 38 extend from exterior end wall 22, through interior wall 21, through center support brackets 23, 25 and 27 and finally through end wall 24. Ducts 38A and 38B lie in a common horizontal plane. While ducts 38 may be constructed either parallel or perpendicular to inlet auger 17, the disclosed and preferred construction provides that the ducts 38 are parallel to the inlet auger 17.

Thus, fabrication of the dryer is less complicated, fewer exhaust ducts are required and air flow from the hot air inlet ducts 28 to exhaust ducts 38 is enhanced.

Exhaust duct 38A is shown located immediately above inlet duct 28B. Ducts 38 have a diamond shaped cross section with the upper vertical apex 37 of the duct 38 an equal vertical distance above the apices 41 and 43 adjacent apex 37. Upper side surfaces 47 and 49 of duct 38 are inclined at substantially the angle of repose of the grain being dried. For example, the angle of repose will be approximately 42 45 for wet corn.

Thus, the downward flow of grain is not impeded by this construction.

All the side surfaces of duct 38, including upper side surfaces 47 and 49, are perforated along that portion of duct 38 between walls 21 and 24. The perforations permit passage of air flow only. Thus, grain is deflected and does not pass through duct 38. Ducts 38 are not perforated between end wall 22 and support wall 21 so that exhaust air can flow and be discharged from the bin without passing back into the chamber defined by interior wall 21 and exterior wall 22. This chamber includes the 'heating elements and other means for providing hot air to ducts 28 and cold air to ducts 40.

Shutters 57 (57A-57B) mounted on exterior end wall 22 are manually adjustable to control the ratio of air flow from the exhaust ducts 38. Similar'shutters (not shown) are provided at the opposite end of ducts 38 in wall 24. The percentage of air flow out duct 38 is dependent upon the position of the shutters 57. When the shutters 57 are opened or raised to" their highest position, the percentage of exhausting air flow through duct 38 is greatest. Conversely, when the shutters 57 are closed or in their lowest position, the percentage of air flow out duct 38 is negligible and all exhaust takes place through ducts 44. The desired percentage of air flow up and out ducts 38 is dependent upon many factors, among the most important being the ambient temperature of the incoming cold air and the grain. The following table illustrates these values and the appropriate relative flow of hot air that exhausts through duct 38.

Outdoor or of fluid flow of fluid flow Ambient Temperature upward through downward through duct 38 duct 44 This data relates to a grain dryer capable of drying approximately 450 bushels per hour by removing 10 percentage points of moisture, with a hot air inlet flow rate of approximately 24M cfm, the upper exhaust duct 38 area being approximately 16 percent of the intermediate exhaust duct 44 area. Two upper exhaust ducts 38A, 388 were utilized as having their apices aligned respectively with the apices of inlet ducts 28B and 28D, respectively.

While ducts 38 may be parallel or perpendicular to inlet auger 17, fewer ducts and associated shutters 57 are required when the ducts are in a parallel relationship with inlet auger l7.

OPERATION In operation, the bin is filled with grain by a feed conveyor (not shown) feeding grain inlet auger 17. After the bin is filled, the metering rolls 45 commence operation to continuously move grain through the bin. Simultaneously, the fan blade 56 shown in FIG. 1 is rotated, thereby forcing air from external the dryer through the space defined between walls 21 and 22 and through the various inlet ducts 28 and 40. A heating coil and burner arrangement 65 located adjacent the inlet ducts 28 heats the air flowing into ducts 28. The heating arrangement 65 normally includes an LP gas vaporizer and burner combination.

The heated air flows into ducts 28A through 28E where it is directed downward via baffles (not shown) into the bin. As in the prior art, the hot air flows downwardly concurrent with the grain flow. However,

in addition, a portion of the hot air also flows upwardly in a countercurrent direction to the grain flow. This upward flow preheats the grain. The percent of air flow upward is dependent upon the position of shutters 57 located at the ends of ducts 38 as hereinbefore described. It is this countercurrent flow of the heating medium which tends to preheat especially cold and wet grain, prevent scorching and to provide better conditioned grain when the hot air begins its concurrent flow downward with the grain to, exhaust ducts 44. In this manner, the coldest grain at the auger inlet 17 is subjected to hot fluid medium which has cooled somewhat in relation to the hot air at the inlet duct 28. Therefore, the coldest grain is not subjected to the hottest air. The hottest air introduced at duct 28 will contact the preheated grain which has flowed past duct 38. In this manner, the grain is not subjected to large temperature differentials.

Alternate embodiments of the present invention may be provided which are still within the intended scope of the invention. For example, inlet ducts 28 might be per forated at surfaces 33 and 34. Heated air may then flow directly upwardly from duct 28 as well as downwardly.

The addition of hot air exhaust ducts 38, though a simple and economical change, has alleviated a problem long present in continuous flow, column type grain dryers. As previously stated, the countercurrent flow of hot air to preheat the especially cold and wet grain has the advantage that the hot air moves up wardly through the cool grain so that at the point where the grain is introduced into the bin, the hot air from ducts 28 has been slightly tempered bycoolness and wetness of the downward moving grain. Thus, the temperature differential between the cold and wet grain and the hot fluid medium is small initially and increases gradually as the grain flows downward towards the source of the hot fluid medium inlet.

What is claimed is:

1. In a portable, continuous flow, grain dryer of the type having an enclosed bin with a wet grain inlet at the top of said bin and grain outlets at the bottom of said bin including a plurality of spaced, parallel horizontal hot fluid inlet ducts for directing a fluid drying medium downwardly through a bed of grain in said bin, a plurality of spaced, parallel, horizontal cold fluid inlet ducts for directing a fluid cooling medium upwardly through said bed of grain, said cold fluid inlet ducts positioned parallel to and below said ho t fluid inlet ducts and spaced from one another to provide a plurality of grain discharge outlets from said bin, fluid inlet means at one end of said inlet ducts, means for adding wet grain through said wet grain inlet, means for withdrawing dry grain from said grain outlets, a first set of horizontal exhaust ducts means intermediate said hot and cold fluid inlet ducts and perpendicular thereto to receive and exhaust fluid medium flowing from said hot inlet ducts in a concurrent direction to grain flow and also exhaust cold fluid medium flowing from said cold inlet ducts in a countercurrent direction to grain flow, each of said exhaust duct means having outlets through said bin on opposite sides thereof and means for providing hot fluid to said hot. inlet duct inlets and cold fluid to said cold inlet duct inlets, the improvement comprising:

a second set of horizontal exhaust duct means above and parallel to said hot fluid inlet ducts and extending through opposite ends of said bin, said second set of exhaust duct means positioned to receive and exhaust a portion of said hot fluid medium flowing from said hot inlet ducts in a countercurrent direction to grain flow thereby preheating said wet grain immediately after it enters said bin.

2. The improvement of claim 1 wherein said duct member includes shutter means to control the amount of fluid flow exhausting through said duct member.

3. The improvement of claim 1 wherein said duct member has a diamond-shaped cross section.

4. The improvement of claim 1 wherein said duct member includes at least two surfaces joined at an apex, said surfaces defining inclines of substantially the angle of repose of the grain being dried.

5. The improvement of claim 1 wherein said second exhaust duct means comprises a pair of parallel duct members intermediate said hot inlet ducts and said wet grain inlet. 

1. In a portable, continuous flow, grain dryer of the type having an enclosed bin with a wet grain inlet at the top of said bin and grain outlets at the bottom of said bin including a plurality of spaced, parallel horizontal hot fluid inlet ducts for directing a fluid drying medium downwardly through a bed of grain in said bin, a plurality of spaced, parallel, horizontal cold fluid inlet ducts for directing a fluid cooling medium upwardly through said bed of grain, said cold fluid inlet ducts positioned parallel to and below said hot fluid inlet ducts and spaced from one another to provide a plurality of grain discharge outlets from said bin, fluid inlet means at one end of said inlet ducts, means for adding wet grain through said wet grain inlet, means for withdrawing dry grain from said grain outlets, a first set of horizontal exhaust ducts means intermediate said hot and cold fluid inlet ducts and perpendicular thereto to receive and exhaust fluid medium flowing from said hot inlet ducts in a concurrent direction to grain flow and also exhaust cold fluid medium flowing from said cold inlet ducts in a countercurrent direction to grain flow, each of said exhaust duct means having outlets through said bin on opposite sides thereof and means for providing hot fluid to said hot inlet duct inlets and cold fluid to said cold inlet duct inlets, the improvement comprising: a second set of horizontal exhaust duct means above and parallel to said hot fluid inlet ducts and extending through opposite ends of said bin, said second set of exhaust duct means positioned to receive and exhaust a portion of said hot fluid medium flowing from said hot inlet ducts in a countercurrent direction to grain flow thereby preheating said wet grain immediately after it enters said bin.
 2. The improvement of claim 1 wherein said duct member includes shutter means to control the amount of fluid flow exhausting through said duct member.
 3. The improvement of claim 1 wherein said duct member has a diamond-shaped cross section.
 4. The improvement of claim 1 wherein said duct member includes at least two surfaces joined at an apex, said surfaces defining inclines of substantially the angle of repose of the grain being dried.
 5. The improvement of claim 1 wherein said second exhaust duct means comprises a pair of parallel duct members intermediate said hot inlet ducts and said wet grain inlet. 